Layout of a reference generating system

ABSTRACT

A layout of a voltage/current reference system is disclosed. A first voltage/current reference circuit (for example, a bandgap reference circuit) and a second voltage/current reference circuit are respectively laid out on either side of a substrate, such as edges or perimeter sides of the substrate. A reference voltage/current is derived by averaging respective output reference voltage/current values of the first and the second voltage/current reference circuits. Accordingly, the noise influence on the voltage/current reference system is minimized.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to voltage/current referencesystems, and more particularly to a layout of a bandgap referencesystem.

2. Description of the Prior Art

A voltage reference system is an electronic circuit that generates afixed voltage regardless of the loading on the circuit. A bandgapreference (BGR) circuit is a voltage reference circuit for generating afixed reference voltage that has a value equal to the electron bandgaplevel of silicon (approximately 1.2 volts) and that changes very littlewith temperature. Bandgap reference circuits are widely used inelectronic systems, such as the source driver for a liquid crystaldisplay (LCD).

FIG. 1 shows schematically the layout of a bandgap reference circuit 10,among others, in a conventional mixed analog-digital system 1, whichalso includes at least one high-voltage subsystem 12 and low-voltagesubsystems 14A and 14B. According to the conventional layout shown inFIG. 1, the bandgap reference circuit 10 is laid out in the middle, forexample, between the low-voltage subsystems 14A and 14B, for the sake oflayout symmetry.

As modern integrated circuits become more complex in design and evenmore enormous in size, noise becomes a non-negligible issue, whichaffects either the output reference voltage or current of the bandgapreference circuit 10. FIG. 2 schematically illustrates the noiseinfluence on the bandgap reference circuit 10 in the system 1. A noisesource 120 originating from the high-voltage subsystem 12 and adjacentto the bandgap reference circuit 10 affects the bandgap referencecircuit 10 with noise along various courses 120A and 120B of influence(e.g., west and east courses in the figure). Subsequently, theinfluenced bandgap reference circuit 10 distributes the noise-addedreference voltage/current to the low-voltage subsystems 14A and 14B inthe directions 122A and 122B, causing the low-voltage subsystems 14A and14B to malfunction.

For reasons including that of the conventional bandgap reference circuitnot effectively defending itself against noise, a need has arisen topropose a novel bandgap reference system and layout to minimize thenoise influence on the bandgap reference system and to prevent the noisefrom being distributed.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a voltage/current reference system and its layout to minimizethe noise influence on the voltage/current reference system.

According to one embodiment, a first voltage reference circuit (forexample, a bandgap reference circuit) and a second voltage referencecircuit are respectively laid out on either side of a substrate,preferably on edge sides (e.g., edges or perimeter sides) of thesubstrate. A first conductive power line electrically extends from afirst output reference voltage of the first voltage reference circuit,and a second conductive power line electrically extends from a secondoutput reference voltage of the second voltage reference circuit. Aconductive connecting line is electrically coupled between the firstconductive power line and the second conductive power line. A referencevoltage node on the conductive connecting line is then used to provide areference voltage.

Another embodiment includes a first current reference circuit (forexample, a bandgap reference circuit) and a second current referencecircuit respectively laid out on either side of a substrate, preferablyon edges or perimeter sides of the substrate. A first current source(for example, a mirror circuit) generates a first current according to afirst output reference current of the first current reference circuit,and a second current source generates a second current according to asecond output reference current of the second current reference circuit.The first and the second currents are then added to provide a referencecurrent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically the layout of a conventional bandgapreference circuit;

FIG. 2 schematically illustrates a noise influence on the conventionalbandgap reference circuit;

FIG. 3 illustrates a layout of bandgap reference circuits according toone embodiment of the present invention;

FIG. 4 shows an interconnection between the bandgap reference circuitsaccording to the embodiment of the present invention;

FIG. 5 illustrates the IR (current times resistance) voltage drop effectalong a first power line, a second power line, and an interconnectingnode; and

FIG. 6 shows an interconnection between the bandgap reference circuitsaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 illustrates the layout of a bandgap reference system, including alow-voltage subsystem 34 and a high-voltage subsystem 32 according toone embodiment of the present invention. A noise source 320 may exist inthe high-voltage subsystem 32 or other electronic component(s) on asubstrate 3. The bandgap reference system includes at least two bandgapreference circuits 30A and 30B. The first bandgap reference circuit 30A,the second bandgap reference circuit 30B, the high-voltage subsystem 32,and the low-voltage subsystem 34 together form an electronic (mixedanalog-digital) system that is laid out on the substrate 3 of a chip, aprinted circuit board, or a package. Although the bandgap referencecircuits 30A and 30B are disclosed in the embodiment, it is appreciatedthat the present invention is well adapted to a voltage/currentreference circuit or a reference generating system in general.

In the depicted embodiment, the two bandgap reference circuits 30A and30B have substantially identical architectures. The first bandgapreference circuit 30A and the second bandgap reference circuit 30B arerespectively laid out on sides (e.g., either side) of the substrate 3,and preferably on edge sides (e.g., edges or perimeter sides/regions) ofthe substrate 3. According to the layout in FIG. 3, the noise source 320originating from the high-voltage subsystem 32 (or other electroniccomponent[s]) and adjacent to the bandgap reference circuits 30A and 30Baffects the bandgap reference circuits 30A and 30B with noise mainlyalong the courses 320A and 320B of influence (e.g., west and eastcourses in the figure). Specifically, the first bandgap referencecircuit 30A is subjected to the single course of noise influence 320A,and the second bandgap reference circuit 30B is subjected to anothersingle course of noise influence 320B. In comparison to the layout inFIG. 2, the single bandgap reference circuit 10 in FIG. 2 is subjectedto at least two courses of noise influence 120A and 120B. As a result,each of the bandgap reference circuits 30A and 30B in the embodimentadvantageously is affected with less noise than the single bandgapreference circuit 10 in FIG. 2.

FIG. 4 shows an interconnection between the two bandgap referencecircuits 30A and 30B according to the embodiment of the presentinvention. The interconnected bandgap reference circuits 30A and 30Bwork as a whole to provide a reference voltage to other subsystem(s),such as the low-voltage subsystem 34 (FIG. 3). In the embodiment, afirst conductive (e.g., metal) power line 40A electrically extends froman output reference voltage of the first bandgap reference circuit 30A,and a second conductive (e.g., metal) power line 40B electricallyextends from an output reference voltage of the second bandgap referencecircuit 30B. The first metal power line 40A and the second metal powerline 40B are spaced apart by a distance, and are also laid out on thesubstrate 3 (FIG. 3). The ground line or lines are omitted in the figurefor brevity.

In the embodiment, a conductive (e.g., metal) connecting line,represented by two resistors R1 and R2, is connected electricallybetween the first power line 40A (at node A) and the second power line40B (at node B). The position of the node A or the node B is not limitedto that in the exemplary figure. An interconnecting node C of the tworesistors R1 and R2 is then used to provide a reference voltage, forexample, to the low-voltage subsystem 34 (FIG. 3) or other subsystem inthe entire system. As a result, an average reference voltage of the tworeference voltages out of the bandgap reference system is generated bythe resistors R1 and R2. It is appreciated that electronic componentsother than the resistors may replace the shown resistors, provided thatthe electronic components have the resistivities R1 and R2 respectively.It is further appreciated that the resistivity R1 and the resistivity R2need not be the same.

According to the interconnection of FIG. 4, any mismatch between thefirst bandgap reference circuit 30A and the second bandgap referencecircuit 30B due to manufacture parameter variances can be substantiallyreduced. Specifically, assume that the first bandgap reference circuit30A generates a first deviated reference voltage ΔV₁ due to the noiseinfluence, and the second bandgap reference circuit 30B generates asecond deviated reference voltage ΔV₂ due to the noise influence. Thefirst reference voltage ΔV₁ and the second deviated reference voltageΔV₂ are then averaged by the serial-connected resistors R1 and R2, or avoltage divider. Accordingly, the resultant average deviated referencevoltage ½(ΔV₁+ΔV₂) is substantially less than the deviated referencevoltage ΔV₀ generated by the single bandgap reference circuit 10 (FIG.2), or ½(ΔV₁+ΔV₂)<ΔV₀.

According to the embodiment, the disclosed bandgap reference circuitsand layout can minimize the amount of noise influence on the bandgapreference circuits 30A and 30B, and thus prevent the noise from beingfurther distributed.

In addition to the mismatch problem being improved by theserial-connected resistors R1 and R2 as discussed above, the IR (currenttimes resistance) voltage drop effect along the first power line 40A andthe second power line 40B, respectively, can be improved as well by thesame serial-connected resistors R1 and R2. FIG. 5 illustrates the IRdrop effect along the first power line 40A, the second power line 40B,and the interconnecting node C. Specifically, the first bandgapreference circuit 30A generates the first deviated reference voltageΔV₁, and the voltage at the first power line 40A may be expressed, ingeneral, as ΔV₁−ΣnRI_(n), where n represents the n-th node away from theoutput reference node. Likewise, the second bandgap reference circuit30B generates the first deviated reference voltage ΔV₂, and the voltageat the second power line 40B may be expressed, in general, asΔV₂−ΣnRI_(n), where n represents the n-th node away from the outputreference node. The voltage at the interconnection node C thus hasaverage deviated voltage ½(ΔV₁+ΔV₂−ΣnRI_(n)). Accordingly, the IR dropeffect is substantially minimized by the serial-connected resistors R1and R2, or the voltage divider.

FIG. 6 shows an interconnection between the two bandgap referencecircuits 30A and 30B according to another embodiment of the presentinvention. The interconnected bandgap reference circuits 30A and 30Bwork as a whole to provide a reference current to one or more othersubsystems, such as the low-voltage subsystem 34 (FIG. 3). In theembodiment, a first current source 60A, such as a mirror circuit,mirrors the output reference current of the first bandgap referencecircuit 30A. The mirror circuit 60A, in the embodiment, includes fourp-type metal-oxide-semiconductor (PMOS) transistors connected in series(i.e., serially), and the area of the PMOS transistors 60A is decreasedby half (with respect to the output-stage transistors in the firstbandgap reference circuit 30A) to obtain half of the output referencecurrent. Likewise, a second current source 60B, such as a mirrorcircuit, mirrors the output reference current of the second bandgapreference circuit 30B. The mirror circuit 60B, in the embodiment,includes four PMOS transistors connected in series (i.e., serially), andthe area of the PMOS transistors 60B is reduced in half (with respect tothe output-stage transistors in the second bandgap reference circuit30B) to obtain half of the output reference current. The (first) outputcurrent of the mirror circuit 60A and the (second) output current ofanother mirror circuit 60B are added as a whole to provide a referencecurrent to another subsystem(s), such as the low-voltage subsystem 34(FIG. 3).

According to the embodiment, the first current source 60A and the secondcurrent source 60B together can minimize the amount of noise influenceand IR drop effect on the bandgap reference circuits 30A and 30B, andthus prevent the noise from being further distributed.

Although specific embodiments have been illustrated and described, itwill be appreciated by those skilled in the art that variousmodifications may be made without departing from the scope of thepresent invention, which is intended to be limited solely by theappended claims.

What is claimed is:
 1. A layout of a reference generating system,comprising: at least one first voltage reference circuit and a secondvoltage reference circuit that are respectively laid out on either sideof a substrate, the first voltage reference circuit being separated fromthe second voltage reference circuit in layout by an electronic circuit;a first conductive power line electrically extending from a first outputreference voltage of the first voltage reference circuit; a secondconductive power line electrically extending from a second outputreference voltage of the second voltage reference circuit; and at leastone conductive connecting line electrically coupled between the firstconductive power line and the second conductive power line; wherein areference voltage node on the conductive connecting line is used toprovide a reference voltage; and wherein the conductive connecting lineincludes a first electronic component and a second electronic component,with the reference voltage node being located at an interconnecting nodeof the first and the second electronic components.
 2. The system ofclaim 1, wherein the first electronic component and the secondelectronic component have approximately the same resistivity.